The present disclosure relates to an image sensing device suitable for use in X-ray photography for medical and nondestructive inspection applications for example, and a display system using such an image sensing device.
In recent years, an image pickup unit such as a human chest X-ray photography unit has been developed that derives radiation-based images as electric signals without any intervention of radiographic films. In such an image pickup unit, a field-effect thin-film transistor (TFT) for reading out accumulated signal charges is arranged on each pixel, and electric signals based on the amount of radiation are derived using a pixel circuit including this transistor.
As such a transistor, a transistor employing a single-gate structure such as so-called top-gate type or bottom-gate type has been commonly used. For the above-described image pickup unit that derives radiation-based images, however, it is known that especially when a silicon oxide film is used for a gate insulating film of a transistor, a threshold voltage (Vth) is shifted to a negative-side due to a radiation effect (for example, see Japanese Unexamined Patent Application Publication No. 2008-252074).
Accordingly, a transistor has been proposed that alleviates any shift in a threshold voltage as described above by adopting a so-called dual-gate structure (double-sided gate structure) in which two gate electrodes are provided with a semiconductor layer interposed between (for example, see Japanese Unexamined Patent Application Publication No. 2004-265935).